Physics Investigation Of Resistance

Extracts from this document...

Introduction

Physics Investigation Of Resistance

Aim 1: To investigate how the electrical resistance of a wire changes in relationship to it’s length. Resistance is when these electrons which flow towards the positive collide with other atoms, they transfer some of their kinetic energy. This transfer on collision is what causes resistance.

Key factors: The factors in this experiment are

●The length of the wire

●The width of the wire

●The type of wire e.g. Nichrome

●The temperature of the wire

●The current passing through the wire

The factor I will be changing is the length of the wire, I will keep all the other factors the Same.

Prediction: I think that as the length of the wire increases so will the resistance of it. I also believe that the rate at which the resistance of the wire increases will be directly proportional to the length. I think this because electric current is the movement of electrons through a conductor. In this experiment a metal wire. So when resistance is high, conductivity is low. Metals conduct electricity well because the atoms in them do not hold on to their electrons very well. Free electrons are created, which carry a negative charge, ‘jump’ along the lines of atoms in a wire which are in a lattice structure. Resistance is when these electrons which flow towards the positive collide with other atoms, they transfer some of their kinetic energy. This transfer on collision is what causes resistance.

These indicate that if you increase the width of wire, the resistance increases. As you can see I have taken 5 well space results to give me an accurate perception of the relationship between a width of wire and resistance. To ensure I get an accurate set of results I will always measure the wire exactly.

Results:

This is not a very dangerous experiment but despite this we always handled electricity with care, we kept the current low, handled with dry hands etc.

To calculate my results accurately I have taken three readings for each length of wire and the used the equation

R=V/I

Resitance (Ω) = Voltage (V) / current (I)

to calculate the resistance.

Below is a graph to show my results when investigating how length of a piece of wire effects resistance

I do not think that doing any more results in our experiment would have made it any more accurate. I feel that the only way to make it more accurate would be to use a different method – perhaps were we had a bar that did not bend in place of the wire. We could even use a rheostat in place of the wire, because it is essentially a long coiled wire that is connected at different lengths to change the resistance of the circuit

I will now evaluate my width experiments results.

I don’t think these results were as accurate as they could have been due to the fact that the width of each piece of wire did not vary in any regular pattern. This can be seen by the results in my graph. Also again slight variations in temperature and inaccuracy’s in the equipment could have effected my results . Also the wire not always being perfectly straight could effect my results. To improve this experiment further I could get different width’s of wire that follow a patter for example the width is doubled each time. I think it would be a good idea to use a bar or a rheostat.

This is because it will take the electrons longer to pass from one end of the wire to the other end. This is because the current is slowed down. The longer the wire, the longer the electrons have to stay squashed together and so the longer they take to pass through the wire and therefore the higher the resistance is.

To measure the wire width I would use different widths of the same length and same material of wire e.g. thin , medium and thick copper wire with thin and thick constantin wire. To record the difference in widths I would use the same voltage and measure the resistance for each thickness.

My preliminary results told me that 6 volts was a good voltage to use as it did not burn the wire unlike 10v which did at 20cm. it also taught me that it was best to start the experiment of length from 100cm down to 10cm this way the wire

The wire must then be allowed to cool, so that it is the same temperature that all the experiments are conducted at. Wire diameter: Wire diameter as stated earlier will affect resistance, due to the area through which the electrons may move without collision.

APPARATUS / EQUIPMENT: APPARATUS AMOUNT REASON Voltmeter 1 To measure the voltage of the circuit in volts Ammeter 2 To measure the current of the circuit in amperes. There are two types, one reading from 0 - 1A and the other form O - 2A.